RF-power harvester circuits may be used to harvest ambient radio-frequency (“RF”) signals as a power source in RF-powered systems, such as passive radio frequency identification (“RFID”) tags for example. With some applications, the ambient RF signal resonates with the antenna and the receiver circuits in the harvester circuit to power the RF-powered system. With an RFID tag, for example, the power may be used to enable signal-processing and wireless data transmission between a battery-free RFID tag and a tag reader that the RF-powered system may be comprise of. Use of RF-power harvester circuits, as opposed to a stored energy source (e.g., a battery), can reduce the cost and the weight associated with nano- and micro-electronic components. Use of RF-power harvester circuits may also obviate the inconvenience of charging or replacing the stored energy source. Omission of batteries may also reduce the risk posed by chemical leakage. With biomedical applications (e.g., medical implants), chemical leakage may pose an additional biological infection risk, thus omission of batteries in these systems may reduce such risk.
Typical ambient RF power sources include cellular signals, WiFi, TV broadcast signals, and RFID signals subject to the regulations of a governing body (e.g., F.C.C.), which exist with varying frequencies and power densities. Existing RF-powered systems have limited operational range and computational capability due to the limited ambient RF power that can be harvested from the ambient environment. One of the reasons for this is the low power-conversion efficiency (PCE) of energy scavenging components of the RF-powered system when attempting to harvest power from the limited ambient RF power. For example, with a wireless several-watt RF signal transmitter, existing RFID tags typically have an operational range of only a few meters. Furthermore, their sensing, identification, and/or transmission functions may have to be abridged due to the limited ambient RF power.
Components of a RF-powered system may include power harvesting components and analog/RF front end and digital processing/storage components. Power harvesting components may include rectifiers and DC-DC converters. Analog/RF front end and digital processing/storage components may include amplifiers and A/D converters. Increasing the PCE and power efficiencies of some of these components may increase the operational range and computational capabilities of the RF-powered system as a whole, thereby enabling increase usage within limited ambient RF power environments.